Conventionally, a vehicle such as a wagon and a minivan is provided with, at a side part of its body, a sliding door that is opened and closed in vehicle-front and vehicle-back directions, thereby allowing passengers or merchandise to be easily loaded or unloaded from a side direction of the vehicle. This sliding door can normally be opened and closed by a manual operation. However, in recent years, there is also often found such a vehicle that the automatic opening/closing apparatus is mounted on the vehicle to automatically open and close the sliding door.
This automatic opening/closing apparatus is known as a cable type in which a cable (cable member) connected to the sliding door from the vehicle-front and vehicle-back directions is guided to a driving unit disposed in the vehicle body via reverse pulleys disposed at both ends of a guide rail; the cable is wound around a driving drum (driving rotor) provided to the driving unit; and this drum is driven for rotation by a driving source such as an electric motor so that the sliding door is automatically opened and closed while being drawn by the cable.
In the cable type automatic opening/closing apparatus, when the sliding door is guided along a curve portion of the guide rail and is drawn inside the vehicle body, length of a movement path of the cable is changed, so that a tensioner mechanism is required to absorb the change in the length of the movement path of the cable. For example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2000-8708) discloses a tensioner mechanism comprising a pair of movable pulleys movably mounted on a tension case in a direction of approaching or separating from each other, and a coil spring for biasing the movable pulleys in a direction in which the movable pulleys are brought close to each other, wherein the cable drawn out from the drum is bridged about each of the corresponding movable pulleys.